This invention relates to a process for the synthesis of 2,4,5-trichlorophenol and 2,4,5-trichlorophenoxyacetic acid analytically free of 2,3,7,8-tetrachloro-dibenzo-p-dioxin in analytical tests sensitive to 1 part per billion.
The presently employed technology to produce 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) and 2,4,5-trichlorophenol (2,4,5-TCP) commercially involves the declorination of 1,2,4,5-tetrachlorobenzene with aqueous sodium hydroxide or anhydrous sodium hydroxide in the presence of alcohols under elevated temperatures and pressures to form 2,4,5-TCP according to the flow diagram: ##STR1## Under the conditions of alkalinity, temperature and pressure this process produces between 1 to 100 parts per million of the highly toxic teratogen 2,3,7,8-tetrachloro-dibenzo-p-dioxin (TCDD) according to the reaction: ##STR2##
In the production of 2,4,5-TCP by this process, the TCDD produced is usually separated by careful distillation or by adsorption on activated carbon. However, the TCDD is claimed to be extremely toxic and cannot readily be disposed of. TCDD is a highly stable compound which is difficult to destroy chemically. Waste disposal by burying is difficult and unsatisfactory. Its destruction by incineration is a possibility which is presently being investigated. However, incineration of such a highly chlorinated compound is difficult and presents the possibility of contamination of either the scrubber liquor, the exhaust gas, or any solid residues.
The production of 2,4,5-T from 2,4,5-TCP is by reaction with monochloroacetic acid according to the reaction: ##STR3## Conditions of this reaction are mild in comparison to the hydrolysis step to produce 2,4,5-TCP. Consequently, no measurable new formation of TCDD can be observed in the latter reaction.